1. Modified Pilot Structure for WiMAX PUSC Permutation Scheme Document Number: C80216m-09_1109 Date Submitted: 2009-04-28 Source: Khalid Elwazeer Mohamed Khairy Center for wireless studies Cairo University Giza, 12613 Egypt Re: TGm Call for Contribution on SDD, Rapporteur Chairs report Abstract : Modified pilot structure for WiMAX PUSC permutation scheme, that results in removing the error floor in the BER. Purpose: To achieve higher data rates with higher constellations with improved channel estimations Note: This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat 1

2. MODIFIED PILOT STRUCTURE FOR WIMAX PUSC PERMUTATION SCHEME By: Khalid ElWazeer and Mohamed Khairy 2

3. Outline WiMAX PUSC current pilot structure Studied methods in channel estimation The proposed modified pilot structure Simulation results for both the original and the modified cases Conclusion 3

4. WiMAX PUSC Pilot Structure In PUSC permutation scheme, the OFDM symbol is divided into clusters Each cluster is composed of 14 adjacent subcarriers as shown: 4

5. Studied Estimation Techniques 1D interpolation on single OFDM symbol. 2D cascaded time/frequency interpolation. 2D simplification to the cascaded time/frequency interpolation. 2D MMSE robust filtering based on two OFDM Symbols. 2D MMSE robust filtering based on three OFDM symbols. Cascaded one dimensional time/frequency MMSE robust filtering. Cascaded time interpolation/frequency filtering. Cascaded frequency interpolation/time filtering. 5

6. MMSE Filtering Illustration 6

7. Cascaded Filtering/Interpolation Illustration 7

8. Comparison between studied methods for original pilot structure 8

9. Comparison – cont. 9

10. Pilot Structure Modification From the previous figures, a BER floor exists for high SNRs. This floor is mainly due to the edges of the symbol. The errors occur at the edges because the number of pilots at these edges is insufficient. If enough pilots exist at the edges of the symbol, this floor disappears. Our contribution is mainly for the clusters at the left most and the right most edges of the symbol. 10

11. Pilot Structure Modification – cont. One extra pilot is added in each side of the OFDM symbol, such that after time filtering/interpolation, two successive pilots always exist at both edges. These two pilots are mainly to guard the left-most and right most edges of the symbol, and make them less error prone. 11

12. Proposal Illustration Right Most Cluster Left Most Cluster 12

13. Results for Modified Pilots 13

14. Results for Modified Pilots – cont. 14

15. Conclusion The modified pilot structure removes the BER error floor This modification is very important for future systems with high data rates, in which large constellations (256 QAM for ex.) are used with high SNRs. 15